Energy dissipative mechanism of graphene foam materials

Graphene foam (GrF) is a new kind of multi-porous material with many potential applications owing to its excellent multi-functional properties, especially its dissipation capability. However, both the dissipative mechanism and some experimental phenomena remain poorly understood. Here, systematic coarse-grained molecular dynamic simulations (CGMD) are conducted to study these issues. The typical stress-strain relationships found in experiments under large-strain loading-unloading and small-strain cyclic load are first reproduced. Based on microstructure analysis, three major dissipative mechanisms in the scale of flakes, i.e., rippling, sliding and impacting, are uncovered. The influencing effects of cycle number, strain magnitude and loading rate on dissipation are further investigated. It is found that the much higher dissipation in the first loading cycle is essentially due to drastic flake rearrangements, which decreases to a smaller one in subsequent cycles. In addition, the dissipation increases almost linearly with the strain magnitude in the first cycle, while it increases with a reduced slope in subsequent cycles due to the flake stacking structures. For a given strain magnitude, the dissipation will be enhanced as the loading rate increases. These results deepen our understanding on the dissipative mechanism of GrFs and should be helpful for the development of novel multi-functional graphene-based composites.